Sublimator



Feb- 23 1965 G. c. RANNENBERG ETAL 3,170,303

SUBLIMATOR Filed Aug. 20, 1963 2 Sheets-Sheet 1 FIGJ @QL/MATE vINVENTORS GEORGE C- RANNENBERG JOHN S- L OVELL.

ATTORNEY Feb. 23, 1965 G. c. RANNENBERG ETAL 3,170r'303l SUBLIMATOR 2Sheets-Sheet 2 Filed Aug. 20, 1963 mmUTm United States Patent O3,170,303 SUBLHMATOR George C. Rannenberg, East Granby, and John S.Lovell,

Bloomfield, Conn., assignors to United Aircraft Corporation, EastHartford, Conn., a corporation of Delaware Filed Ang. 20, 1963, Ser. No.303,382 11 Claims. (Cl. 62-64) This invention relates to heat exchangersand particularly to sublimators wherein a uid or surface intended to becooled transfers its heat to a refrigerant which is suhlimated.

It is an object of this invention to provide a heat exchanger comprisinga porous member for receiving a liquid refrigerant and having a surfacesubjected to an at mosphere whose pressure is at a value wherein therefrigerant will sublirnate.

Another object of this invention is to provide a chamber in a heatexchanger for receiving refrigerant, which chamber has a wall formedfrom a porous material containing a surface subjected to a pressure ator below the triple point of the refrigerant.

A still further object of this invention is to provide a cooling systemwhich is characterized as being relatively simple to construct,economical to manufacture, is selfregulating, automatic and highlyreliable but yet capable of rugged use.

A still further object of this invention is to provide a heat exchangerof the sublimator type having a ysupply of refrigerant at a constantpressure and fed into the heat exchanger as a function of the demands ofthe heat exchanger without the use of metering devices, sensors and thelike.

A still further object of this invention is to provide a means ofutilizing an expendable refrigerant in a highly efficient manner, thatis, with little or no loss through carry-over of liquid refrigerant.

Other features and advantages will be apparent from the specificationand claims and from the accompanying drawings which illustrate anembodiment of the invention.

FIG. 1 is a perspective view partly in cross section i1- lustratin g theinvention.

FIG. 2 is an enlarged cross-sectional view of the porous plate.

FIG. 3 is a perspective view partly in cross section illustratinganother embodiment of the invention showing a number of elements groupedtogether to produce a large capacity device.

Heat exchangers of the water boiler class are generally well known inthe art and essentially comprise a heat exchanger core which may storerefrigerant therein or refrigerant may be fed thereto. The fluid mediumintended to be cooled is then passed though the heat exchanger either indirect or indirect heat exchange relation for transferring the heat tothe refrigerant. The refrigerant then absorbing this heat changes state;namely, boils off and is vented to atmosphere or ambient. Inapplications, particularly in aircraft or outer space applications,where it is necessary to assure proper cooling in a most efficientmanner, it is customary to control the amount of refrigerant to maintainthe temperature of the fluid medium intended to be cooled at its desiredvalue. This entails the utilization of valving and sensing mechanismresulting in a relatively complex temperature control system. We havefound that a properly designed heat exchanger utilizing our inventioncan be made to opcrate in an ei'licient manner without using any'sensingand valving mechanism.

While this invention is somewhat like a water boiler, it is in factconsidered by those skilled in the art to be a sublimator. However, itis to be understood that the chambers defined in layer 14.

3,170,303 Patented Feb. 23', 1965 ICC terminology selected in no waylimits the scope of this lnvention.

This invention is particularly applicable where therefrigerant used hasa triple point, that is, where equilibrium of vapor, liquid and solidwill occur at a predetermined temperature or pressure and that there isavailable an environment at or below this condition. The refrigerantwhich may be water, while not limited thereto, is directed to the heatexchanger from a pressurized source, which heat exchanger defines achamber for receiving the refrigerant. One area of the chamber containsa porous or sintered material having a surface exposed to thisenvironment. Therefrigerant passing through the porous material freezeswhen exposed to the low pressure of this environment thus limitingrefrigerant flow therethrough and eventually blocking it olf. Therefrigerant sublimates into this environment as heat is conducted to theporous plate by virtue of being in indirect heat exchange relation withthe fluid medium intended to bevv K undergo a cycle as follows:

Beginning with a solid plug of ice in the passage, sublimation occurs atthe surface exposed to space, and, as a result, subcools the walls ofthe passage. When the thickness of the ice layer is reduced until it canno longer support the internal pressure in the boiler, water begins toiiow through the passage to space. When the liquid water sees pressurebelow Iits triple point and encounters the subcooled passage walls, itfreezes, reforming the plug and completing the cycle. Although operationof a single passage is cyclic, operation of the gross porous plate iscontinuous.

Now referring to FIG. l and FIG. 2 which generally show a heat exchangergenerally indicated by numeral 16B comprising a lower layer 12 andadjacent upper layer 14. The lower layer contains continuous ruffled fin16 sandwiched between end plate 1S and intermediate plate 29. It will benoted that the corrugated fin together with the adjacent plates define aseries of parallel conducting passages for receiving hot fluids intendedto be cooled. The adjacent layer may compri-se similar ruffled finssandwiched between the intermediate plate 20 and the upper plate 22.Refrigerant is fed to the chambers defined by the ruffled plate togetherwith the porous plate 22 and intermediate plate 20 through inlet line 24which feed header 26 and in turn directs refrigerant to the various Inthis embodiment, the porous plate overlies the entire surface of thelayer 14 and is subjected to an atmosphere whose pressure will cause therefrigerant to freeze. It will be understood by those skilled in the artthat the particular shape and configuration of the heat exchanger cantake any form, depending on the particular application for which it isto be used.

As viewed in FIG. 2, as the refrigerant enters into the porous plate andcomes into contact with this low pressure environment, the refrigerantchanges state from a liquid to a solid causing ice to form in the poresof the sintered material. We have found that the ice substantially formsa uniform sheet extending completely across the porous material. Thisice sheet serves to pre- 'vent the flow of refrigerant through theporous plate. The ice sublimates to the low pressure environment,depleting the ice Vin the porous plate and hence changing itsdimensions. This automatically causes additional refrigerant yto ow intothe porous plate for replacing the amount depleted. Consequently, theamount of refrigerant sublimated to atmosphere is replenished byautomatically receiving additional refrigerant fluid from thepressurized source. This results in a self-regulating,

simple type of sublimator.

An example of the conditions of a sublimator used to cool glycol andusing Water as a refrigerant is presented hereinbelow, but is includedherein merely to set forth one such example and in no way is intended tolimit the scope of the invention.

(c) The feed water pressure is at l p,s.i.a. (absolute) (d) The lowpressure source=200 microns vacuum (e) Q Btu/hour A ft.2 (porous plate):1700

FIG. 3 is an exemplary showing of another embodinientv of this inventionwhere the sublimator is generally indicated by numeral 30 comprisingcore32, feed water inlet header 34, exit header S6, fluid intended to becooled, inlet header 38 and its exit header 40. As noted from thedrawing, suitable piping is connected to each header in any well-knownmanner.

The core is made by alternately stacking passes so that a refrigerant(water) layer is in juxtaposition with a layer of fluid intended to becooled. Each layer or pass of the core may be constructed in theconventional manner save for the fact that a porous plate overlies eachof the refrigerant passes. As refrigerant is fed into the feed header 34it passes through the plurality of refrigerant passes. Since all of therefrigerant passes are similarly constructed, for the sake ofconvenience and to facilitate in the explanation of this invention, onlyone refrigerant pass and one fluid-intended-to-becooled pass will bedescribed. The refrigerant pass comprises a continuous ruffled lin 42made from any suitable material such as stainless steel extending thelength and width of the core and sandwiched between intermediate plate44 formed from a suitable highly heat conductive material and porousplate 46 constructed from any suitable sintered or porous material, butpreferably having good heat conductivity properties. A pair of closuremembers 48 (only one is shown) is mounted adjacent opposite the ends ofthe ruffled fins and a pair of closure members 51 (only one being shown)is mounted adjacent the porous plate. The porous plate 46 overlies therutiled fins and as water tends to migrate through the pores it willcome in contact with the low pressure environment to which it is exposedby virtue of the opening of the outlet header 36. It will be noted thatanother closure plate 58 is mounted at the end of iin element 42adjacent the exit header to prevent water from escaping into the exitheader.

The pass for the uid intended to be cooled is likewise constructed fromcontinuous fin element 50, sandwiched between intermediate plates 44 and52. A pair of closure plates 54 (only one being shown) closes off theend thereof. It will be noted that the series of passages defined byruffled fin 50 and the intermediate plates 44 and 52 pass fluid in adirection transverse to direction of the passages defined by ruffled fin42 and its associated intermediate plates.

The operation of sublimator 30 is identical to the operation ofsublimator shown in FIG. l. As water refrigerant is admitted to the corethrough the various refrigerant passes it will migrate through the poresof that porous plate and owing to the fact that it is subjected to a lowpressure, on contact it freezes. This forms a layer of ice extendingacross the porous plate preventing water from discharging. The fluidintended to be Cooled passing adjacent the water pass transmits heatthrough the ns, intermediate plate, through the water and eventuallyinto the porous plate. This heat causes the ice to sublimate whichsublimation occurs at a rate directly proportional to the heat load. Theuid intended to be cooled passes through the heat exchanger giving olfheat as described above and being discharged at a temperature lower thanit entered.

It is to be understood that the invention is not limited to the specificembodiment herein illustrated and described, but may be used in otherways without departing from its spirit.

We claim:

1. Means for automatically self-regulating refrigerant ow from a supplyof refrigerant into a heat exchanger comprising a porous plate having apore size whose magnitude is such that the porous plate is relativelyimpervious to the ow of liquid under normal operating pressure mountedbetween the refrigerant and a substantially low pressure source whosepressure is below the triple point of the refrigerant, said porous platebeing capable of holding the refrigerant in its solid state for defininga closure between the refrigerant in its liquid form and the lowpressureA source, means for conducting heat from a medium intended to becooled to said solid refrigerant for causing said solid refrigerant tosublimate in said low pressure source, whereby said refrigerant isautomatically supplied to said porous plate to replenish the solidrefrigerant sublimated to said low pressure source.

2. A sublimator comprising a pair of chambers, a heat transfer surfaceforming a side of the lirst of said chambers, said first of saidchambers containing a fluid to be cooled, the second of said chamberscontaining a refrigerant Huid, a porous wall having pore openings in theorder of 1/2 micron forming one side of said second chamber remote fromand parallel to the first chamber, said porous wall forming a path forrefrigerant fluid to flow from the inside to the outside of saidrefrigerant chamber, a pressure on the outside of said porous wallsufciently low to maintain the refrigerant iiuid in said porous wall inits solid state, and means for supplying refrigerant to said secondchamber.

3. Apparatus for cooling a fluid or surface by a refrigerant having atriple point comprising a chamber for receiving said refrigerant, aporous plate having a pore size in the order of 1/2 micron forming awall surface of said chamber and having one face thereof subjected to alow pressure environment at or below said triple point, said porousplate exuding refrigerant to the low pressure environment whereby saidrefrigerant upon contact therewith solidifes in said porous plate, saidchamber being located adjacent the fluid or surface intended to becooled so that heat absorbed by said refrigerant sublimates said solidrefrigerant to the low pressure environment, a source of refrigerantincluding connection means leading refrigerant to said chamber.

4. An automatic, self-regulating sublimator comprising a source ofwater, a chamber, means interconnecting said source and said chamber forcontinuously feeding water thereto, a porous member forming a wall ofsaid chamber and in contact with said water defining a path forconducting water to fiow from the inner surface to the outer surfacethereof, said outer surface being subjected to a low pressure sourcewhose pressure is below the triple point of the water so that uponcontact with said low pressure source said water freezes in said porousmember, and a medium intended to be cooled located adjacent saidchamber, an open ended chamber having a heat transfer surface disposedparallel to and opposite said porous member for receiving said medium,means between said porous plate and said heat transfer surface toconduct heat from one to the other whereby heat conducted from saidmedium is absorbed by the frozen water causing said water to sublimateto said low pressure source..

arr/0,303

V5. A self-regulating sublimator having arst chamber v, adapted toreceive fluid intended to be cooled, an ad-V v jacent second chamberadapted to receive a refrigerant,

having a triple point, in its liquid state, a low pressure source whosepressure is below the triple point of the refrigerant, a porous plateformed from a sintered material having a pore size in the order of 1/2micron detining lone of the walls of said second chamber mountedlbetween said chambers and said low pressure source defining a flow pathfrom the inner to outer surface of said porous plate, said porous plateholding said refrigerant in its solid statewhen subjectedto said lowpres-sure forY dening'a sheet ofsolid refrigerant extending the lengthVand width of the porous plate for blocking off the ow of said liquidrefrigerant through said porous plate to said source, wall meansdisposed parallel to said porous plate formed from conductive materialbetween saidl rst and second chambers for transferring heat to saidsolid refrigerant from said fluid intended to be cooled to cause saidsolid refrigerant to sublimate to said low vpressure source, and meansfor conducting liquid `reyfrigerant to said porous plate.

'erant so that said refrigerant freezes therein, and placing saidrefrigerant adjacent said uid `or surface intended to Vbe cooled wherebyheat is transferred from said fluid or surface causing said frozenrefrigerant to sublimate.

7. Apparatus for automatically self-regulating refrigerant flow from asupply of refrigerant into a heat exv changer comprising a porous memberhaving its pore sizes in the order of '1/2 micron mounted between therefrigerant and a substantially low pressure source whose pressure isbelow the triple point of the refrigerant, said porous member beingcapable of holding the refrigerant in its solid state for dening aVclosure between the refrigerant in its liquid form and the low pressuresource, means including a heat transfer surface disposed parallel tosaid porous plate for conducting heat from amedium intended to be cooledto said solid refrigerant for causing said solid refrigerant to-su'olimate in said low pressure source, whereby said refrigerant isautomatically supplied to said porous member to replenish the solidrefrigerant sublimated to said low pressure source.

8. Apparatus as delined in claim 7 wherein said refrigerant is water.

9. Apparatus as defined in claim 7 wherein said means also includes afin element disposed between 4said porous member and said heat transfersurface:

10. Apparatus as dened in claim 7 wherein said porous member is formedfrom a metallic material.

l1. Apparatus as defined in claim 7 wherein said porous l member isformed from stainless steel.

References Cited by the Examiner UNITED STATES PATENTS 1,556,734 10/25Taylor 62-'224 2,960,847 11/60 P6aer 63-314 2,990,696 Y 7/61 Fisher62-314 3,014,353 12/61y scu11y,eta1. 62-467 A ROBERT A. OLEARY, PrimaryExaminers

6. THE PROCESS OF COOLING A FLUID OR SURFACE COMPRISING THE STEPS OFCONDUCTING A REFRIGERANT HAVING A TRIPLE POINT TO A POROUS PLATE HAVINGA PORE SIZE IN THE ORDER OF 1/2 MICRON PERVIOUS TO SAID REFRIGERANT,PASSING THE REFRIGERANT THROUGH SAID POROUS PLATE, SUBJECTING SAIDREFRIGERANT TO A PRESSURE AT OR BELOW THE TRIPLE POINT OF SAID REFRIG-